26 The Philippine Journal of Science i9i6 



position, but rather mechanical mixtures of several compounds. 

 Hydraulicity does not depend entirely upon the ultimate chemical 

 composition, upon the presence of opaline silica, nor upon the 

 presence of water of hydration. In the light of present knowl- 

 edge it seems as though hydraulicity depends upon a number 

 of factors, which apparently vary with the material. The 

 mineralogical composition of the tuff is an important factor in 

 this connection and has been overlooked by several investigators. 

 To be able conclusively to prove the cause of the induration under 

 water of pozzuolanas or tuffs when mixed with lime involves 

 a study of the minerals present in the original material before 

 mixing with lime and a study of the compounds and minerals 

 formed after mixing and the addition of water. With the aid 

 of the mineralogical microscope it would be possible to identify 

 such compounds as are formed. 



PREPARATION OF THE RAW MATERIALS 

 TUFF 



The entire sample of tuff, amounting to about 272 kilograms, 

 was first reduced in a jaw crusher to the size of a hazelnut 

 and then fed into a gyratory grinder. The product from the 

 gyratory grinder was comminuted to a fineness of approximately 

 80 per cent through the 200-mesh sieve. No difficulty was en- 

 countered during the reduction process. Although considered 

 locally as a hard tuff, the material, judged from a technological 

 standpoint, is very soft. During the preliminary reduction in 

 the jaw crusher, what especially attracted my attention was the 

 apparent ease with which the tuff was disintegrated; there was 

 an entire absence of flying fragments, sharp snapping, and 

 straining of machine parts, such as are characteristic when 

 crushing even a soft limestone. The softness of the material 

 would be of considerable advantage in case the tuff were used 

 commercially in the manufacture of a pozzuolan cement; grind- 

 ing costs could be maintained at a minimum. The tuff was not 

 dried, but was ground just as taken out of the quarry. Analysis 

 showed 3.09 per cent moisture. The sample was collected during 

 the dry season, which accounts for the comparative absence of 

 water. 



LIM£ 



The lime used was made from Montalban limestone in the 

 Bureau of Science experimental kiln. This stone is hard, fine 

 grained, and has grayish to bluish and yellowish tinges. An 

 analysis made by F. B. Beyer, formerly chemist of the Bureau 

 of Science, gave the following composition : 



